This invention pertains in general to the art of wire or filament manufacture. Specifically, the invention is a wire accumulator for use in a wire or filament manufacturing facility, particularly for a wire or filament having low tensile strength and which is therefore easily broken, such as, for example, an optical fiber.
A typical manufacturing facility may include a machine for drawing an optical fiber, a first take-up device downstream of the drawing machine, a tensile strength testing machine for testing the tensile strength of the optical fiber during its travel, and a winding device for winding the optical fiber on a bobbin. Optical fibers are relatively weak filament and are therefore easily broken in the tensile strength testing machine. It is, therefore, usual to provide an accumulator and a second take-up device between the first take-up device and the tensile strength testing machine to facilitate replacement of the, optical fiber without stopping the drawing machine if the fiber is broken. Commonly assigned U.S. application with Ser. No. 502,059 filed on June 7, 1983, now abandoned, is directed to such an accumulator. The invention set forth in this application is a further improvement over this accumulator.
Referring now to FIGS. 1-4 there is shown a known accumulator. Optical fiber 1 is drawn into the accumulator at a constant speed from a drawing machine (not shown) by a first take-up device 2, past guide rollers 17 and to a second take-up device 9 via dancer rollers 11 which control the speed of optical fiber on the second take-up device. From second take-up device 9, the fiber is subjected to a tensile strength test by a tensile testing machine 27, and wound by a winder (not shown) downstream of dancer rollers 28 which control the winding speed, as shown by arrows in FIG. 1. The accumulator includes two groups Y and Z of cylindrical accumulating guide rollers 3 and 3' which are rotatably supported on bearings 5 and shafts 6 and 6' secured at equal intervals in a circular array to side plates 7 and 8, and 7' and 8', respectively, as shown in FIGS. 1 and 2. Each guide roller 3 and 3' is formed around its outer periphery with a plurality of grooves 4 which are equally spaced apart from one another at a pitch P. The grooves 4 on the guide rollers 3 or 3' are slightly displaced axially from one guide roller to another, as shown in FIG. 2. A shaft 14 extending through the center of the guide roller assembly Z is rotatably supported by bearings 12 on a stand 10. A variable speed motor 13 is provided at one end of the shaft 14 for driving it, and an arm 15 is secured to the other end of the shaft 14. A guide bar 16 is secured to the outer end of the arm 15. Moving blocks 18 and 18' are slidable transversely along the guide bar 16 as shown in FIG. 3. Guide rollers 17 and 17' for distributing optical fiber to the accumulating guide roller assemblies Y and Z are rotatably carried on the blocks 18 and 18', respectively. A screw shaft 21 is rotatably supported by bearings 20 on the support members 19 and 19' secured to the opposite ends of the guide bar 16 and the arm 15, and extends in parallel to the guide bar 16. The screw shaft 21 has threaded portions 22 and 23 on both sides of the arm 15, and they are fastened to the moving blocks 18 and 18' by nuts. Threaded portion 22 has a right-hand screw, and threaded portion 23 a left-hand screw. Each screw has a pitch which is equal to pitch P of the grooves 4 on the guide rollers 3 and 3'. Thus, each rotation of the screw shaft 21 causes the movement of the moving blocks 18 and 18' in opposite directions by a distance equal to the pitch of the grooves 4. A timing belt pulley 24 is provided on screw shaft 21 and connected by a timing belt 26 to a timing belt pulley 25 provided on the side plate 7 of the guide roller assembly Y coaxially with the shaft 14, as shown in FIGS. 1 and 4. The two timing belt pulleys have a rotation ratio of 1:1.
If the optical fiber drawing machine is in normal operation, optical fiber passes through the first take-up device 2, the distributing guide rollers 17 and 17', the second take-up device 9 and the tensile testing machine 27 without winding about rollers 3 and 3', and is wound on the winder (not shown), as shown by the arrows in FIG. 1.
If the optical fiber is broken in the tensile testing machine 27, the second take-up device gradually reduces its speed, and simultaneously, the variable speed motor 13 is driven to rotate the shaft 14 in the direction of an arrow R in FIG. 1. The rotation of the shaft 14 causes the rotation of the arm 15 and the distributing guide rollers 17 and 17' about the accumulating guide roller assemblies in the direction of an arrow Q in FIG. 4 thereby winding and accumulating optical fiber on the accumulating guide roller assemblies. As the timing belt pulley 25 on the side plate 7 and the timing belt pulley 24 on the screw shaft 21 are connected to each other by the timing belt 26, the screw shaft is caused to rotate relative to the blocks 18 and 18' in the direction of an arrow T in FIG. 1 by the same angular distance as that of the rotation of the shaft 14. As a result, screws 22 and 23 cause the right-hand movement of the distributing guide roller 17 and the left-hand movement of the guide roller 17'. As the pitch of the screws is equal to that of the grooves on the accumulating guide rollers, the rotation of the shaft 14 results in the orderly distribution, winding and accumulation of optical fiber in the grooves 4 of the accumulating guide roller assemblies. The second take-up device, which has gradually reduced its speed, reaches stability at a constant speed. Optical fiber is withdrawn at a low speed and guided manually to the winder through the tension testing machine. The rotating speed of the variable speed motor 13 is adjusted so that the difference in take-up speed between the first and second take-up devices may effect accumulation of optical fiber. When the apparatus is brought back to its normal operating condition, the second take-up device is rotated at a higher speed than the first take-up device and motor 13 is rotated in the opposite direction, so that optical fiber may be released from the accumulator. The speed of the optical fiber leaving the second take-up device is, therefore, the sum of the take-up speed of the first take-up device and the speed of the optical fiber released from the accumulator. If all of the accumulated optical fiber has been released, the speed of the second take-up device is lowered to coincide with that of the first take-up device, i.e., of the drawing machine. Thus, any breakage of optical fiber in the tensile testing machine can be rectified without lowering the speed of the drawing machine or stopping it.
The apparatus as hereinabove described has, however, a number of disadvantages. As the shafts 6 and 6' for the accumulating guide rollers 3 and 3' are fixed, the bearings 5 are subjected to a high degree of frictional resistance, and as the guide rollers for accumulating optical fiber are caused by the optical fiber to rotate at a speed coinciding with the traveling speed of the optical fiber to be accumulated, the guide rollers impose on the optical fiber an increased tension which may result in breakage, or a worsening of its properties even if it may not be broken. Moreover, the inertia of the guide roller causes a change in the tension of the optical fiber whenever the rotating speed of the guide rollers is varied.
FIG. 5 shows an improved accumulator. The accumulating guide rollers are fixed to shafts 6 and 6'. The guide roller assembly Y is rotated by timing belts 35 and 37 via timing belt pulleys in such a way that the peripheral speed of the grooves on the rollers may coincide with the speed of the optical fiber on the first take-up device 2. The shafts 6' for the guide roller assembly Z are driven as a result of operation by a differential gear assembly 42 on the speed of optical fiber on the first take-up device and the speed of accumulation by the rotation of the arm 14. Thus, the peripheral speeds of the guide roller assemblies Y and Z are always maintained equal to the speed of optical fiber traveling past them.
As the FIG. 5 arrangement uses a differential gear unit, its backlash creates an instantaneous speed change in the guide roller assembly Z and it causes a change in the tension of a wire or filament on the distributing guide rollers. As the accumulator comprises a plurality of guide rollers equally spaced apart from one another in a circular array, the wire or filament which is accumulated has a polygonal shape, and therefore, the wire or filament on the distributing guide rollers is subjected to the same number of pulsing speed changes as that of the sides of the polygon during each rotation about the accumulator when it is accumulated or released. This causes a change in the tension of the wire or filament on the distributing guide rollers.
It is necessary to prevent such tension changes from occurring when the manufacturing process requires the maintenance of a low tension which does not make any appreciable change. The conventional system employs electrical control by the variable speed motor 13 of the speed of the optical fiber to be accumulated or released, and also requires the electrical control of the take-up speed of the second take-up device 9. An error is likely to develop between these two kinds of control. The correction of this error requires a complicated system, as it is necessary to correct the speed of the second take-up device 9 by the speed control dancer rollers 11.